Automatic gas analyzer



D. v. MosEs x-:TAL 2,551,281

AUTOMATIC GAS ANALYZER Ma1y11, 1951 2 Sheets-Sheet l Filed Nov. 29, 1944 M www? May l, 1951 D. v. MosEs ETAL 2,551,281

AUTOMATIC GAS ANALYZER Filed Nov. 29, 1944 y 2 Sheets-Sheet 2 cAmET HEATER I l f11 I; cuNsrAN TIMER E V-voLTAE cLAmPmG i: '9 soLENorDs, i l

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Patented May 1, 1951 STATES PATENT OFFICE AUTOMATIC GAS ANALYZER corporation of Delaware Application November 29, 1944, Serial No. 565,738

Claims. (Cl. 23-255) y This invention relates to gas analysis and an instrument for automatically recording the amount of a gas present in a gaseous mixture. More particularly the Ainvention is concerned with determining and recording intermittently the concentration of hydrogen sulde or other gas to be measured by passinga gas through a chemically impregnated gas permeable tape or ribbon and measuring the light reilecting power thereof.

It is known that hydrogen sulfide will react with lead acetate to give a black precipitate varying in intensity with the amount of sulfur reacting with the lead acetate. It is also commonly known that the depth in color will cause a corresponding change in light absorption of appropriate Wave length. Advantage has been taken of these principles in known recording analyzers in which a measured fio-w of gas containing a r-eactive constituent is contacted with color forming materials in solution, with a subsequent automatic measurement of light absorption furnishing the actuating electrical differential for a recording mechanism. An improvement in such analyzers is disclosed in the D. V. Moses et al. U. S. Patent, 2,232,622 of February 18, 1941. The instant case is a further modication and improvement particularly directed to the continuous analysis of minute quantities o1 a gas in a gaseous mixture of it.

An object of the invention is to provide an improved method of gas analysis and novel means for its accomplishment. Another object is to provide gas analyzing means responsive to color changes resulting from passing a gas through a chemically impregnated gas permeable tape. Still another object is to measure by comparison a chemically stained tape and an unstained tape by a new and novel mechanism and to provide a process whereby it is operated. Yet another object is to provide a highly active gas by humidifying it prior to its analysis.

Other objects and advantages of the invention will hereinafter appear.

These objects are accomplished according to the invention, particular features and advantages of which will be apparent from a consideration of the accompanying drawings and the ensuing description. As has been emphasized in the related patent, gas permeable tape impregnated with color forming material possesses many advantages over the formerly used solution Contact methods. The rate of flow and duration of iiow of the gas being measured through the tape makes it possible to measure very small amounts of hydrogen sulfide or other gas, amounts undetectable by devices heretofore employed.

There follows a description of one of the numerous embodiments of the invention in which the same number is given to similar parts throughout the description. Referring to the drawings:

Fig. 1 is a perspective view of the assembled device.

Fig. 2 is a sectional view along line A-A of Fig. 1, of a gas collector and photccel arrangement.

Fig. 3 is a wire diagram of the electrical circuit containing the photocells and recorder unit.'

Fig. 4 is a wire diagram of the electrcal power system used for the lighting source and for the actuation and control of the tape movement.

With reference now to Fig. l, which illustrates the device mounted in a cabinet I6, vmovable tape 6 passes through the top thereof. The tape 5 is made of a gas permeable chemically treated fabric as, for example, an -un-inked typewriter ribbon which has been previously air-dried after being treated with an aqueous solution containing 10% lead acetate, 5% acetic acid and 15% glycerine. Tape is supplied from roll 24, the turning of which is resisted by a spring brake 25 acting on wheel 2t which is fixed to revolve with roll 25. A suitable cover, not shown, protects the tape from atmospheric contamination.

The tape t is positioned lengthwise between the gas contactor Il and the gas collector i8. Movement of the tape 6 is initiated by rollers 54 and 55, roller 54 being driven by motor 2l through the pulley and spring belt arrangement 28. The spring belt arrangement 28 provides a flexible connection between motor 2l and roll 54 allowing slippage when necessary, the spring belt 28 being driven by a pulley so geared to the motor 2l that it revolves at the rate or" about 60 R. P. M. A projection 29 is Xed to one end of roll 54 and operatively engages a projection integral with a gravity operated mercury (Mercoid) switch 30, the projection 2$ is so arranged that it engages the projection on the Mercoid switch 30 once during each revolution of roll 54.

The gas handling system comprises a metering and pressure regulating apparatus of wellknown type, not shown, which regulates and indicates the volume of gas supplied, a bubbler-bottle 2 containing a saturated aqueous solution of ammonium nitrate which maintains a definite rela-- tive humidity of less than a trap 3 either empty or packed with an inert material such as glass wool for removal of entrained mist or dust and the required connections. The gas handling andl conditioning equipment is enclosed in the upper compartment of cabinet i6, enclosure not l shown, and the temperature in this compartment is maintained at a denite temperature say 35 C. by a suitable means such, for example, as by an electrical resistance heater H and a therinal switch 56, see Fig. 4.

The optical system a light source, duplicate light filters and duplicate condensing lenses. The light bulb 9 supplied with current from the constant voltage transformer il, is mounted in a parabolic reilector i8, which is in turn mounted on lever arm i2. The lever arm is arranged so that the light beam may be tilted whereby the proportion of light delivered to duplicate `blue illters, i3, with a wave length of approximately 450 millimicrons (although other suitable wave length may be used), mounted in the iloor of the upper compartment of cabinet i6 serve to transmit the rays to the duplicate condensing lenses iii. The lters serve to enhance the dierence in reflectivity between unstained and stained tape. The condensing lenses ill gather light from the filters I3 and focus the beams through the center openings in the center of photoelectric cells ill and iii (see Fig. 2) in such a manner that essentially all of the lower surfaces of the tape above the openings 3i and 32 are covered by the lightbeain. Reflection from the tape is projected on the upper active surface o the photoelectric cells 4Q and di. Current generated in the photoelectric cells is transmitted by appropriate connections to the recorder 2 i.

Timers 22 and 2S serve to institute and terminate the cyclic action ci' the analyzer which will be described later.

Fig. 2 shows a cross section taken lengthwise of the gas contacter Il and the gas collector i8 along line A-A of Fig. 1. The tape 6 covers compartments 3l and S2 in the gas contactor Il and compartments 33 and '54 in the gas collector i8, and extends beyond the edge or" each compartment suhciently to provide a gastig'ht seal when the gas collector i8 is clamped against gas contacter Il and the tape is thereby pressed against the upper contactor face by the gaskets 35 which are xed on the lower gas collector face i8. Small rims 52 and 53 on the edge of compartments 3l and 32 serve to stretch the tape smoothly over the openings when clamped. Clamping of the tape is accomplished by actuating the dual solenoids i8 which transmit their downward tension to the gas collector E8 via the extension rods and wingnut arrangements 2d.

Compartment-s Si and 32 in the gas contactor il are covered in a gastight manner at their lower extremity by transparent windows .'55 and respectively. Underlying the windows 36 and 3l are contact rings 38 and 35 which make electrical contact with the active upper faces of the barrier layer photcelectric cells it and di respectively. A second pair o contact rings i2 and i3 make contact with the lower races of the photoelectric cells il and 4i, respec ively. The essembly is sealed against atmospheric contamination by a second pair of transparent windows ifi and i5 and foil `wer rings 156 and Lil. Appropriate electrical outlets, not shown, communicate with the contact rings 38, Si?, d2 and 33. The complete assembly which covers compartment 3i is shown as i5 on Fig. l and is termed the standard photocell in the description of the method of operation which follows. Likewise the assembly which covers compartment 32 is designated as 5 on Fig. l and termed the primary photocell.

Compartment 32 through which gas is passed is fitted with a gas inlet 4 and a circular gas distributing space 43, 2, covered in a gastight manner by a cylinder of impervious material i3 which is perforated with a series of small distributing orifices 5B. A baiiie of transparent material 5i aids gas distribution. Compartment 34 is tted with a vent I which may be connected with a suitable means of disposal for the waste gas.

Operation of the apparatus for the detection ci hydrogen sulfide in a gaseous mixture containing it is as follows: A metered iiow of the gas is passed at a constant rate through inlet i into humidier 2 where it is adjusted to a relative humidity of about 60%. The gas then passes through trap 3 and connection 4 into distributing ring t8 through orilices 5S and through impregnated tape 5 where it produces a stain propor tional in depth to the hydrogen sulfide concentration in the gas and the quantity of the gas allowed to pass through the system while the tape is exposed. rThe waste gas passes into compartment 3S and through vent l.

Light from the bulb 9 passes through the filters i3, the condensing lenses i4 and through the photocell assmblies I5 and 5 to the tape. Reflection of the light from the tape 6 to the photoelectric cells iii.) and il causes electrical impulses which are transmitted to the recorder 2|. In the recorder these impulses are electrically subtracted so that the movement of the recorder and the resulting record represents the difference between the current flow from the standard photoelectric cell i5 exposed to reection from the unstained tape and the current flow from the primary photoelectric cell 5 exposed to reflection from the stained tape. By the application o proper factors determined experimentally, this dierence is converted to terms of the hydrogen suliide concentration. This may be eiected by the use of standard gases containing known amounts of hydrogen sulde or other gas being measured. It is readily possible to determine the amount of movement produced in the recorder 2i by various concentrations and to construct a scale or chart from which concentrations in any of the standard units of expression, such as grains of hydrogen sulfide per cubic feet of gas can be read directly.

At the end of the measurement cycle, timer 23 disconnects the driving power from the recorder causing the recorder pen actuating mechanism to remain stationary. The recorder clock 2l mechanism, however, continues to function. Gas continues to flow without interruption. At the end of this idle period which may vary from a few minutes to a few hours depending on the desired time between observations, timer 22 actuates the solenoid of switch 30 which breaks .the circuit to the clamping solenoids I9 which hold contactor Il and collector I8 tightly clamped together allowing the compressed springs 3 to separate them suillciently to permit the tape to move freely. Simultaneously the motor 21 is started driving the roll 54 and causing the exposure of fresh sections of tape on compartments 3i and 32. When the roller 54 has made approximately one revolution the projection 29 engages the switch 3a which disconnects the motor and reconnects the clamping solenoids again clamping the tape and stopping its movement. At this time timer 23 is reset and started on its repeat cycle. Drift of the motor is allowed to cause slippage in the spring belt 28. The timer 22 resets itself during the operation of switch 30 after a slight delay provided by a 'magnticmercuryswitch. Another cycle is then commenced. The period of the cycle and the period of tape exposure may be varied by adjustment of the timers. A wide range of hydrogen sulfide concentrations may be covered by cycle changes and by varying the gas flow as required.

The photoelectric cells 5 and I5 and the recorder circuit is illustrated by Fig. 3. rihis circuit comprises essentially a continuous balance potentiometer `circuit wellknown in the recording instrument field. A standard photoelectric cell I5 provides the source of reference voltage. A photocell shunt resistance 6I is placed in parallel with a fixed resistance 52 and a slide Wire resistance 63. Opposing this arrangement is the primary photocell 5 with its shunt resistance-65, the voltages between the standard photocell I5 and the primary kphotocell 5 being opposed across the main slide wire 53 as shown. The values of the photocell shunt resistance 6I and 65 together with that or" the fixed resistance 62 are chosen in such a manner that when the photocells 5 and I5 are both exposed to reilection from unstained tape, the potentials are balanced with the main slide in the so-called zero position at the lower end of slide wire resistance 63. When the primary cell 5 is exposed to the reiiection from stained tape the system is unbalanced causing a current to flow. This current is converted to alternating current by converter 66, is amplified and passed through a motor, not shown, which resets the slide to the new position necessary to rebalance the potentials in the system. The position of the slide required to balance the potential is recorded on a moving chart, not shown. It is to be understood that the above description of the recorder is typical only and that any potentiometric recorder of well-known type possessing the required sensitivity may be used.

Fig. 4 is a diagram of the electrical power system in the analyzer and illustrates the connections to the various component parts. The light bulb 9 is supplied with current from the ccnstant voltage transformer II which is connected to the 110 volt power lines 51 and 58. The cabinet resistance heater 'I'I is connected to power line 58 and through the thermoswitch 56 to power line 5l. The chart motor of the recorder 2| is connected to the power lines 5l and 53. The power supply to the balancing motor in recorder 2i is controlled by timer 23 which is connected to 5'! and via the mercoid relay St to 58. Clamping solenoids i9 are connected to 51 and via mercoid relay 3E! to 58. rlihe tape motor 21 is connected to 5l and via the mercoid relay to 58. Timer 22' is connected to the two power lines 5l and 5B, to the solenoid of the mercoid relay 30 and to time delay 19. The time delay is interposed in the timer circuit in such manner that a slight delay is produced which gives the time necessary for automatic resetting of timer 23 and relay s0.

The electrical changes occurring during an analyzer cycle are as follows: At the start of the measurement period the clamping solenoids I9 are energized, the recorder 2i is operating to measure and record the electrical impulses transmitted to it and both timers 22 and 23 are functioning to measure their respective time intervals. At the end of the measurement, timer 23 opens the power circuit to the balancing motor of recorder 2I causing the indicating pointer and recorder pen to remain stationary at their last position. The chart actuatingl mechanism of recorder 2| continues to function. This-idle period, in which no observations are taken, is chosen a1; will and may vary from minutesto hours as the occasion demands. At theend of the idle period, timer 22 actuates closing the circuit to the solenoid of relay 30. The time. delay 'Iiiy functions to allow time for the relay 3ll'to function and for timer 22 to reset. The relay 30 then opens the circuit to the clamping solenoids i9 and to timer 23 which resets. The motor circuit is closed and the motor 2l starts. Motor 2l' continues to operate until the projection 29 (see Fig. l) actuates relay 3@ in a reverse direction from the foregoing. This energizes the clamping solenoids is, and timer 23 and disconnects the motor '21. Energizing of the timer 23 starts the balancing motor in the recorder and sets conditions for a repeat cycle.

During operation of the analyzer the tem- .peratureof the cabinet enclosing the measuring equipment is controlled to some temperature above atmospheric by action of the thermoswitch 56 and resistance heater 1I.

As will be appreciated by those skilled in the art the recorder may be used for detecting small amounts of a gas in a mixture containing it. Illustrating examples include:

l. A recording instrument for gas analysis involving tape travel and tape impregnation phases of a detecting cycle, comprising in combination a tape color sensitive to a gas, an exposure chamber subdivided by the tape into a gas inlet compartment and ya gas exit compartment, means for passing the tape between the compartments, means for passing gas through the compartments and through the tape subdividing the chamber, a photoelectric cell positioned in the gas compartment opposite `and in direct View of the tape whereby the color intensity of the tape is measured by the photoelectric cell during the tapes impregnation with the gas being analyzed, said compartments being capable of restricted movement apart to permit the tape freedom to pass between the compartments during the tape travelling phase and movement together to hold the tape by the juxtaposition oi the compartments during the tape impregnating phase of the detecting cycle.

2. A recording instrument as described in claim l which includes timing means constructed and arranged for adjusting the time of exposure of the tape during the impregnation phase of the detecting cycle.

3. A recording instrument as described in claim l which includes timing means constructed and arranged for starting and stopping the travel of the tape to permit adjustable delay of periods between observations of the impregnated tape.

4. A recording instrument for gas analysis involving tape travel and tape impregnation phases of a detecting cycle, comprising in combination a tape color sensitive to -a gas, an exposure chamber subdivided by the tape into a gas inlet compartment and a gas exit compartment, means for passing gas through the compartments and the tape positioned between the compartments, means for passing the tape between .the compartments, a photelectric cell positioned in the `inlet gas compartment opposite and in direct view of the tape whereby the color intensity of the tape is measured by the photoelectric cell during the tapes impregnation with the gas being analyzed, the compartments cooperating with means to dene a space permitting the tape to run freely therethrough during the tape travelling phase, and holding the tape therein as a diaphragm between the compartments during the impregnating phase of the detecting cycle.

5. A recording instrument for gas analysis involving tape travel and tape impregnation phases of a detecting cycle, comprising in combination a tape color sensitive to a gas, an exposure chamber divided by the tape into lower gas inlet and upper gas exit compartments, the upper compartment being mounted for restricted movement away from the lower compartment to provide free passage of the tape during the tape travelling phase and in juxtaposition on the lower compartment to hold the tape as a diaphragm between the the compartments during the impregnating phase of the detecting cycle, a photoelectric cell positioned in the gas exposure chamber opposite yand in direct View of the tape whereby the color intensity of the tape is measured by the photoelectric cell during the tapes impregnation with the gas being analyzed.

DOUGLAS V. MOSES.

JOHN W. BRUMBAUGH.

REFERENCES CITED The following references are of record n the file of this patent:

UNITED STATES PATENTS Number Name Date 2,113,063 Stryker et al Apr. 5, 1938 2,232,622 Moses et al Feb. 18, 1941 2,345,090 Brace Mar. 28, 1944 OTHER REFERENCES Instruments, vol. 14, page 214, July 1941. 

1. A RECORDING INSTRUMENT FOR GAS ANALYSIS INVOLVING TAPE TRAVEL AND TAPE IMPREGNATION PHASES OF A DETECTING CYCLE, COMPRISING IN COMBINATION A TAPE COLOR SENSITIVE TO A GAS, AN EXPOSURE CHAMBER SUBDIVIDED BY THE TAPE INTO A GAS INLET COMPARTMENT AND A GAS EXIT COMPARTMENT, MEANS FOR PASSING THE TAPE BETWEEN THE COMPARTMENTS, MEANS FOR PASSING GAS THROUGH THE COMPARTMENTS AND THROUGH THE TAPE SUBDIVIDING THE CHAMBER, A PHOTOELECTRIC CELL POSITIONED IN THE GAS COMPARTMENT OPPOSITE AND IN DIRECT VIEW OF THE TAPE WHEREBY THE COLOR INTENSITY OF THE TAPE IS MEASURED BY THE PHOTOELECTRIC CELL DURING THE TAPE''S IMPREGNATION WITH THE GAS BEING ANALYZED, SAID COMPARTMENTS BEING CAPABLE OF RESTRICTED MOVEMENT APART TO PERMIT THE TAPE FREEDOM TO PASS BETWEEN THE COMPATMENTS DURING THE TAPE TRAVELLING PHASE AND MOVEMENT TOGETHER TO HOLD THE TAPE BY THE JUXTAPOSITION OF THE COMPARTMENTS DURING THE TAPE IMPREGNATING PHASE OF THE DETECTING CYCLE. 